Advances over the last several decades in medical and habilitative technologies have dramatically increased the life expectancy of mentally retarded people. Because of their increased lifespan, large numbers of older retarded adults must now cope with developmental changes associated with old age. While considerable effort has been directed at investigating many relevant issues, there is a paucity of information available regarding the influences of aging on basic cognitive processes in this population. However, as studies of nonretarded adults have repeatedly shown, the speed of cognitive processes underlying performance decreases as a result of normal aging. Retarded adults are likely to experience similar declines in their information processing speed. The indirect impact of any loss in processing efficiency on everyday behavior could be more severe than for their nonretarded peers, who have greater compensatory cognitive resources. The proposed research will determine how aging affects the speed of mental processes of adults with mild to moderate mental retardation (40 to 70 IQs) without Down syndrome, ages 54 to 74, and compare their performance to that of younger retarded adults (ages 40 to 48) and nonretarded adults of equal age. In addition, because adults with Down syndrome exhibit many indications of precocious aging, the performance profiles of retarded adults with and without Down syndrome will be compared to determine if age-associated slowing of information processing speed occurs earlier in the Down syndrome population. A cross-sequential design will be employed, with performance of all subjects assessed four times at one year intervals. The investigators will recruit as subjects 192 retarded adults without Down syndrome, 48 with DS, and 140 nonretarded adults (total n = 380). Each test cycle will include a test of visual activity and 4 experimental protocols requiring subjects to perform various two-choice ("same/different") reaction time (RT) tasks. Experimental tasks consist of well researched protocols embedded within full color animated graphics routines developed in the PI's laboratory. These procedures will provide subjects with a stimulating context, concrete communication of task demands, and effective trial by trial feedback and reinforcement. Data obtained from the four protocols (correct RTs and percent errors) will provide a set of converging measures of the rate at which subjects can compare symbols and will permit quantification of age-associated changes in processing efficiency within the older adult mentally retarded population. The four different protocols to be tested are presented within the context of a 'space invaders' type game. Helicopters appear on the screen and descend to capture the subjects attention. The helicopters are then overwritten by a square that contains stimuli for comparison. Subjects must then make a same or different response by pressing one of two buttons. If they are correct, the helicopter on the side of the button they pressed explodes. It the subject is wrong, the screen goes blank and an appropriate warning message is spoken by the computer.